Conventionally, a crawler travel device that has on its left and right sides endless belts suitable for travel on uneven ground are used in construction machines, civil engineering machines, agricultural machines, transport vehicles, etc. The crawler travel devices include: a pair of crawler frames, each of which supports an endless belt; a center frame disposed between the crawler frames; and an upper rotating body placed on the center frame.
The center frame includes as main components: a center member supporting the upper rotating body, and front and rear legs disposed on the left and right sides of the center members. The upper rotating body is composed of work equipment, a cabin, a driver's seat, an engine, a control device, etc.
The center frame includes a center member and front and rear legs formed separately or integrally.
As an example of the configuration in which a center member and legs are separately formed, a center frame (refer to the Patent Document 1) or suchlike has been proposed in which a center member is formed from a steel plate and hollow legs are formed from hollow circular pipes or by bending a steel plate.
Only a box-like portion defined by a center member in the present invention is called “a center frame” in the Patent Document 1. Crawler frames, legs, a center front plate, and a center rear plate in the present invention are called “side frames,” “legs,” “a front plate,” and “a rear plate” respectively in the Patent Document 1. However, in the description of the configuration of the Patent Document 1 in this specification, the above-mentioned terms used in the present invention will be quoted.
However, “a central portion” in the Patent Document 1, which may correspond to the box-like portion defined by the center member in the present invention, is quoted as is because the present invention does not use an equivalent term. The center member in the present invention is divided into the upper plate, and left and right plates referred to in the Patent Document 1, and these terms “upper plate” and “side plate” are used as necessity requires.
As shown in FIG. 15, the center frame described in the Patent Document 1 includes: a central portion 50; left and right crawler frames 51, which are disposed on the left and right sides of the central portion 50; a pair of front legs 52 and a pair of rear legs 53 connected to the central portion 50.
The central portion 50 is formed from a substantially rectangular steel plate or suchlike. Side plates 56, a center front plate 57, a center rear plate 58, etc., are fixed between the upper plate 54 and lower plate 55 by welding. Thus, the central portion 50 has the form of a box-like structure. Further, in order to accommodate a center joint (not shown) and so on, a through-opening 59A is made vertically in the central portion. 50 of the upper plate 54.
Each of the crawler frames 51 is composed of an intermediate frame 60, an idler wheel bracket 61, a motor bracket 62, etc. A crawler 51 is wound around each crawler frame 51 and between the idler wheel and driving wheel.
The left and right front legs 52 secured to the side plates of the central portion 50 by welding are formed from pipes of hollow circular cross-section. The leading end of each of the front legs 52 is securely welded to the side plate 63 of the intermediate frame 60 of the crawler frame 51. The rear legs are formed from pipes of hollow circular cross-section as in the front legs 52. Each of the leading ends of the rear legs is securely welded to a corner between the center rear plate and the corresponding side plate 56 of the central portion The other end of each of the rear legs 53 is securely welded between the rear portion of the intermediate frame 60 of the corresponding crawler 51 and the connection flange 64 on the corresponding motor bracket 62 side.
The Patent Document 1 discloses another configuration of the center frame, and each of front legs 65 and each of the rear legs 66 in this configuration are shown in FIG. 16. In this configuration, the upper plates of the front and rear legs 65 and 66 are formed by bending a steel plate into a trapezoid by a press molding means, and a lower plate 67 is welded to the ends of the bent upper plates.
As a configuration in which a center member and legs are integrated, a center frame (refer to Patent Document 2) has been proposed in which a center member and legs are integrally formed by casting means, pressing means, or forging means.
A track frame in the present invention is called “a crawler frame” in the Patent Document 2. In addition, the center frame, crawler frame, center member, and lower plate in the present invention are called “a machine frame,” “a track frame,” “a center frame,” and “a bottom frame” respectively in the Patent Document 2. However, quoting the terms mentioned above in the present invention, the configuration of the Patent Document 2 will be described.
As shown in FIG. 17, in the track frame 70 described in Patent Document 2, crawler frames 74 are disposed on the left and right sides of the center frame 76. The center frame 76 includes a center member 71, and front legs 72 and rear legs 73 integrally formed on the left and right sides of the center member 71. In the center frame, a top, side walls, and the pairs of legs are integrally molded by a molding means so that the bottom of the center frame is open. A lower plate 75 is securely welded to the bottom of the center frame.
Patent Document 1: Pamphlet of International Application No. 03-042022
Patent Document 2: Japanese Patent Application Laid-Open No. 2005-255141